1. Field of the Invention
This invention relates to generation of high amplitude standing waves, fluid pumps and refrigerators and, more specifically, to thermoacoustic cooling engines.
2. Description of the Related Art
Over the past fourteen years, there has been an increasing interest in the development of acoustical cooling engines for a variety of commercial, military and industrial applications. Interest in thermoacoustic cooling has escalated with the ban in production of chlorofluorocarbons (CFCs) which was imposed at the end of 1995 under the terms of the Montreal Protocols. Thermoacoustic cooling is an attractive alternative due to the fact that it can use inert gases. These gases do not participate in chemical reactions and are therefore neither toxic nor flammable. They do not contribute to stratospheric ozone depletion, global warming, production of acid rain, or any other environmental degradation that could lead to domestic or international legislative restrictions now or in the future.
Prior to this invention, all electrically driven thermoacoustic cooling engines have used a stationery resonator which was driven by a vibrating pistons. S. L. Garrett, "ThermoAcoustic Life Sciences Refrigerator: A preliminary design study," NASA Tech. Report No. LS-10114, L. B. Johnson Space Center, Life Sciences Directorate, Houston, Tex. (Oct. 30, 1991); S. L. Garrett, J. A. Adeff and T. J. Holler, "Thermoacoustic Refrigerator for Space Applications," J. Thermophysics and Heat Transfer, Vol. 7, No. 4, pp. 595-599 (1993); S. L. Garrett, "High-Power Thermo-Acoustic Refrigerator," U.S. patent application Ser. No. 08/520,974 U.S. Pat. No. 5,647,216 (Jul. 15, 1997)!. This choice of excitation required (i) a motor mechanism (which has typically been an electrodynamic drive which is similar to conventional loudspeakers), (ii) an elastic suspension system to provide resonant cancellation of the driver/piston moving mass, and (iii) a flexure seal, such as a metal bellows, that isolated the front surface of the piston, which would drive the thermoacoustic load, from the out-of-phase volumetric velocity of the opposite surface, which could cancel the desired effects of the front surface.
In previous designs these three functions were combined in a driver single unit. This forced compromises which did not permit the separate optimization of the individual functions. Since the suspension had to be housed with the voice-coil/magnet structure of the electrodynamic motor mechanism, the size and design of the suspension "springs" were limited. The number and type of suitable alternative motor mechanisms were also severely constrained in previous designs. If a motor was located outside the pressurized resonator, then another flexible seal was required to bring the force of the external motor into the pressurized thermoacoustic resonator. The requirement for a flexible piston seal which could withstand the fatigue induced by one-hundred billion cycles over a fifteen-year lifetime limited the available piston excursion and the acceptable differential pressure across the flexure seal.